Thanks for the Andre_f1 track conversions! Your tracks have some issues:
-missing shadows, if the texture is transparent (trees) you have to set the AlphaRef to 0.5
-make a double of the guard rails, doubleside them and don´t forget to remvoe the key 1wall (else the cars get stucked into the guard rails
-use Alpha Croma (not alpha blending) for the guard rails with transparent texture , else you can look through them